Gaseous electric discharge tube



Feb. 13, 1962 G. J. EKKERS ETAL 3,021,446

GASEOUS ELECTRIC DISCHARGE TUBE Filed May 16, 1955 jWgM 29 M WM INVENT0R.

BY Jam, .L M. Mm

Ar fio fiE Y5 United States Patent 3,021,446 GASEGUS ELECTRIC DISCHARGE TUBE Gyshert Jacob Ekkers, Wettingen, and Aldo Patriarea,

Laufohr, near Brugg, Switzerland, assignors to Patelhold Patentverwertuugs- 82 Elektro-Holding A.G.,

Giarus, Switzerland Filed May 16, 15155, Ser. No. 503,343 Claims priority, application Switzerland May 15, 1954 4 Claims. (Cl. 313204) The present invention relates to gaseous electric discharge tubes and particularly those of the grid-controlled type.

It has been known to be advantageous to fill the interior of such tubes with a vapor of an alkali metal. However, when this has been done it has been found most ditlicult to control primary emission from the grid element. During operation of the discharge tube, the control grid absorbs a metal layer, e.g. cesium, which very strongly diminishes the work function for electrons. At control grid temperatures of about 300 C. the grid emission is already so large that the grid either loses entirely its ability to control the discharge instant of the tube or the required grid control force becomes unbearably high. Forced cooling of the grids is a possibility to overcome these diificulties but is not economically feasible, because of the high costs involved, in low-priced tubes of relatively low output.

In accordance with the present invention, primary emission from the control grid is controlled and practically fully suppressed by the novel expedient of covering the surface of the control grid either completely, or for the most part with an insulating i.e. electrically non-conductive material.

In the drawings which illustrate a typical embodiment of the invention;

FIG. 1 is a view in central vertical section of the electric discharge device with the non-conductive, insulating coating on the control grid; and

FIG. 2 is also a view in central vertical section illustrating a modified construction for the improved discharge tube.

With reference now to FIG. 1 the gaseous discharge tube is seen to be made of glass and is normflly circular in transverse cross-section. Tube 19 is filled with a vapor of an alkli metal such as cesium and encloses a cathode 11, an anode 12 and a control grid 13 of annular configuration. The entire surface of grid 13 is covered by a layer 14 of non-conductive material. One suitable material for the coating layer 14 is corundum (A1 0 since it is not attacked by the cesium metal vapor, and it has a very slight vapor tension and also possesses a high melting point. However, other clays, i.e. zirconia or beryllium oxide or their mixtures can be used equally as "ice well. Sinterable corundum can be easily applied to grid 13 by soaking or spraying, and subsequently it can be sintered to a hard, well adhesive coating through thermal processing. The coating material 14 also covers the leadin support conductors 15 completely down to the point where these seal to the tube wall.

It has been proven in practice that the invention, namely the coated control grid, makes it possible to reduce the disturbing grid emission in the tube down to about one-thousandth of its former current magnitude. Thus the grid emission for gaseous discharge tubes filled with a vapor of an alkali metal can be brought down to that level usumly found in gaseous discharge tubes filled with mercury vapor or with an inert gas.

In the modified embodiment illustrated in FIG. 2 the construction is substantially the same as in H6. 1 except that the inner peripheral surface 16a of the annular control grid 16 is left uncovered by the non-conductive layer 17. 'It has been found in practice that even with the inner peripheral surface portion 16a of the control grid 16 exposed to the alkali metal vapor there is no appreciable increase in grid emission over that which obtains with the FIG. 1 embodiment.

In conclusion it will be understood that various changes in the specific constructions illustrated may be made without however departing from the spirit and scope of the invention as defined in the appended claims. The control grid itself may be of different configuration and the lead in supports for the grid will have to be protected by the electrically insulative coating only in those instances where made from a material which heats appreciably.

We claim:

1. In an electric discharge tube having cathode, anode and control grid elements and filled with an alkali metal vapor, the improvement wherein the surface of said control grid element is covered at least for the most part with a non-conductive material.

2. An electric discharge tube as defined in claim 1 wherein said non-conductive material is sintered corundum.

3. An electric discharge tube as defined in claim 1 wherein said control grid is constituted by an annular plate completely covered by said non-conductive material 4. An electric discharge tube as defined in claim 1 wherein said control grid is constituted by an annular plate, said plate being covered by said non-conductive material except for the inner peripheral surface portion thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,518 Smith Nov. 29, 1938 2,484,837 Lake Oct. 18, 1949 2,504,231 Smith Apr. 18, 1950 

